What is DSP?According to the
term, Digital Signal Processing (DSP) refers to electronic processing
of signals such as radio, microwaves, sound, video, image, protocols,
control logic and data.Digital Signal
Processors (DSPs) characteristics make them suitable for many purposes
like real-time data communication, high-quality graphics processing,
audio-video enhancement, fast algorithm implementations and rapid
numeric processing applications. DSPs are essentially
fast number-crunchers. Their features include which high speed-to-size
performance, comparatively low-cost and low-power consumption. DSP features include
providing ADC functionality and fast processing, as explained below. Data and Control
signals on Wireless carriers are in analog form, and they need to be
converted to digital mode to treat the information discontinuously, as
a discrete series of binary numbers. The goal of digital
signal processing is to use the power of digital computation to manage
and modify the signal data. Therefore, the first stage in many DSP
systems is to translate smooth real-world signals into a digital
approximation. This translation is accomplished by an
Analog-to-Digital Converter (ADC). After successful and complete
translation, the data points give a detailed and accurate rendering of
the signal. After removing irrelevant frequencies, the ADC passes its
digitized signal information to a DSP, which does the bulk of the
processing. Eventually, after signal processing and ‘conditioning’ the
digital data may be turned back into an analog signal, albeit one that
is quite different from and much improved over the original.In Wireless domain,
DSP filters the noise from a baseband signal, remove unwanted
interference from Wireless carrier, amplify audio and baseband
frequencies and suppress others, encrypt (For example, Scramble
cellular phone conversations to protect privacy) or decrypt
information using algorithms and techniques, or analyze a complex wave
form into its spectral components for Wireless carriers. Basically, digital
signal processing is highly numerical and very repetitive and the
primary challenge is the speed requirement for DSP systems to work in
real time, capturing and processing information as it happens. In
Wireless devices and systems, ADCs and DSPs must keep up with the work
flow. If they fall behind, information is lost and the signal gets
distorted. For example, in Wireless devices or units, ADC must fetch
the signal samples fast enough to catch all the relevant fluctuations.
Imagine trying to record a 2-minute video of a ‘Live’ football game
with a GPRS mobile phone (with inbuilt camera) running at one frame
per second. If the ADC isn’t fast enough, the film would be
incoherent, missing entire plays in the intervals between frames. The
DSP must also keep up the pace, computing out calculations as fast as
the signal data is received from ADC. While playing digital audio
(Polyphonic ringtones, MP3 files, FM Radio) on your mobile phone, the
stereo equipment handles sound signals of up to 20 kilohertz (20,000
cycles per second, the upper limit of human hearing), requiring a DSP
to perform hundreds of millions of operations per second. In case of
satellite phones, the signal from satellite transmissions are even
faster, reaching up into the Gigahertz (billions of cycles per second)
range!

DSP Processors (DSPs)DSP devices are often
differentiated based on small to large calculations that are processed
for the application. Generally the processor’s capacity is based on
the size of data it can handle for processing and the type of
arithmetic computations it is capable of DSP Processors used
in applications like telecommunications and wireless units are
generally 16-bit, 24-bit, 32-bit. Needless to say 32-bit processor has
a wider dynamic range as compared to others. Similarly two types of
arithmetic computation which DSPs can handle are fixed point and
floating point, where the latter has a higher dynamic range. The
System Designer can decide on which processor will be best suitable
for the application where the DSPs will be applicable.

Some of
the examples include:

Application

DSPs preferred

Reasons

Wireless units / Cell phones (Voice
only)

16-bit fixed-point

Works on relatively narrow range of
sound frequencies

Mobile units / Cell phones with
in-built MP3 player

24-bit fixed-point with 16-bit or
24-bit ADC

Hi-fidelity stereo sound with wider
range

Mobile units / Cell phones with
in-built camera to capture still pictures and video in color

32-bit floating-point

Much greater dynamic range for image
processing, high quality gaming

DSP in Wireless environmentThere are many
constraints for wireless devices and systems which fall into
consideration, like low power design and power control, when we
consider the signal processing aspects. Wireless is an area
where DSP plays a very important role, especially in the field of
baseband processing and even microprocessing.Wireless
Signal Processing is extensively
included in systems like GPS, CDMA, WLAN, Multimedia Messaging, etc.
Multimedia Messaging includes a potential area of DSP, i.e. Image
Processing, Audio and Video Processing. Nowadays, all newly launched
cellular and mobile phones are Multimedia enabled. By the year end
2005, the global percentage of multimedia-enabled phone users is
expected to grow above 90%.

RF Issues for Wireless Systems
Wireless personal and mobile cellular communications are expected to
be one of the hottest growth areas of 2000 and beyond. They have
enjoyed the fastest growth in the telecommunications industry – adding
customers at a rate of 20-30% globally in the Area of Wireless
communications, a year. Presently, at least six satellite systems are
being developed so that personal voice and data communications can be
transmitted from any part of the earth to another using a simple,
handheld device. These future systems will provide data and voice
communications to anywhere in the world, using a combination of
wireless telephones, wireless modems, terrestrial cellular telephones
and satellite phones. The use of wireless remote sensing, remote
identification, direct broadcast, global navigation and compact
sensors has also gained popularity in the past decade. Wireless
communications and sensors have become a part of consumer’s daily
life. All of these wireless systems consist of a radio frequency (RF)
or microwave front end.

Antennas for Wireless Communications – Sounds Obvious!
From mobile telephones to wireless Internet access to networked
appliances and peripherals, there is an increasing reliance on
wireless communications to provide or enhance functionality for
products and services. The wireless communications industry continues
to generate new products and applications for consumers and new
opportunities for businesses. The enormity of the opportunities
presented by the current explosion of wireless applications is
accompanied by comparable design and manufacturing challenges.
The world of wireless communications can appear to be a confusing
offering of services, products and standards, all competing for
dominance in a dynamic marketplace. But regardless of modulation,
protocol, bandwidth or frequency, every wireless device requires an
antenna for transmission and/or reception.
The antenna is often taken for granted, but its performance is
critical to the successful operation of any wireless system. Three
major areas of activity in antenna research and development have
emerged to meet the needs of modern communications systems: size
reduction, wideband or multi-band operation, and adaptive pattern
control.
Now, we shall look into the
following topics which are considered mainly while designing a
Wireless Device or Unit –